Figure 4.

Dose dependence of amplitudes of global Ca²⁺ spikes induced by caged IP₃ or ACh. (A and B) Semilog plots of [Ca²⁺]_i immediately (0.24 s) after photolysis of caged IP₃ in the trigger zone ([Ca²⁺]_t) (A) and in the basal area ([Ca²⁺]_b) (B), respectively. The smooth curves were drawn assuming median effective concentrations of 5 and 50 μM, respectively. (C and D) Semilog plots of peak [Ca²⁺]_i in the trigger zone ([Ca²⁺]_t) versus [IP₃]_i (C) or ACh concentration (D). The smooth curves were drawn assuming median effective concentrations of 10 and 0.5 μM for IP₃ and ACh, respectively. (E and F) Correlations between peak [Ca²⁺]_i in the trigger zone ([Ca²⁺]_t) and that in the basal area ([Ca²⁺]_b) for global Ca²⁺ spikes induced by IP₃ or ACh, respectively. The regression coefficients are 0.57 and 0.63 for IP₃ and ACh, respectively.